Convert signal from Phototransistor to logic level

[Futterama]

Hello forum,

I'm using a phototransistor-based reflective object sensor to measure the RPM of a fast rotating wheel. I get this output from the phototransistor (see attachment) which will be 1kHz max. (60,000 RPMs max.).

How do I convert that signal to something useful for a microcontroller (PIC12F675)?

Regards,
Futterama

 

[Roff]

Does the average DC level vary with changes in ambient light, supply voltage, temperature, or phase of the moon, or is there some sort of feedback system to keep it constant?

I'm thinking AC coupling into a comparator, but that will only work if the detector never saturates (or cuts off) due to one or more of the above considerations.
You would probably have a better outcome if you posted schematics, so we can see what you're starting with.

 

[audioguru]

I've never seen a phototransistor biased halfway like that. Usually it is cutoff and conducts a little with radiation. Maybe he looked at it on a 'scope set for AC.
Then he just needs a two transistor amplifier. The first one with cap-coupling on its input and a variable gain control on its emitter, and the 2nd transistor to saturate and cutoff fully from the 5V supply. :lol: